Inkjet printer with contractable chamber

ABSTRACT

An ink jet nozzle assembly for an inkjet printer, having a nozzle and an actuator for ejecting ink through said nozzle; wherein, the actuator has a resiliently contractable chamber. The chamber is a series of arcuate vanes arranged in an annular form around the nozzle opening. Actuation of a thermally expandable member forces the vanes to slide against each other to contract the chamber in the same manner of as an iris.

FIELD OF THE INVENTION

[0001] The present invention relates to ink jet printing and inparticular discloses an iris motion ink jet printer.

[0002] The present invention further relates to the field of drop ondemand ink jet printing.

BACKGROUND OF THE INVENTION

[0003] Many different types of printing have been invented, a largenumber of which are presently in use. The known forms of printing have avariety of methods for marking the print media with a relevant markingmedia. Commonly used forms of printing include offset printing, laserprinting and copying devices, dot matrix type impact printers, thermalpaper printers, film recorders, thermal wax printers, dye sublimationprinters and ink jet printers both of the drop on demand and continuousflow type. Each type of printer has its own advantages and problems whenconsidering cost, speed, quality, reliability, simplicity ofconstruction and operation etc.

[0004] In recent years, the field of ink jet printing, wherein eachindividual pixel of ink is derived from one or more ink nozzles hasbecome increasingly popular primarily due to its inexpensive andversatile nature.

[0005] Many different techniques of ink jet printing have been invented.For a survey of the field, reference is made to an article by J Moore,“Non-Impact Printing: Introduction and Historical Perspective”, OutputHard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

[0006] Ink Jet printers themselves come in many different forms. Theutilization of a continuous stream of ink in ink jet printing appears todate back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hanselldiscloses a simple form of continuous stream electro-static ink jetprinting.

[0007] U.S. Pat. No. 3,596,275 by Sweet also discloses a process of acontinuous inkjet printing including the step wherein the ink jet streamis modulated by a high frequency electro-static field so as to causedrop separation. This technique is still utilized by severalmanufacturers including Elmjet and Scitex (see also U.S. Pat. No.3,373,437 by Sweet et al)

[0008] Piezoelectric ink jet printers are also one form of commonlyutilized ink jet printing device. Piezoelectric systems are disclosed byKyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes adiaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970)which discloses a squeeze mode of operation of a piezoelectric crystal,Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode ofpiezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses apiezoelectric push mode actuation of the ink jet stream and Fischbeck inU.S. Pat. No. 4,584,590 which discloses a shear mode type ofpiezoelectric tansducer element.

[0009] Recently, thermal ink jet printing has become an extremelypopular form of ink jet printing. The ink jet printing techniquesinclude those disclosed by Endo et al in GB 2007162 (1979) and Vaught etal in U.S. Pat. No. 4,490,728. Both the aforementioned referencesdisclosed ink jet printing techniques which rely upon the activation ofan electrothermal actuator which results in the creation of a bubble ina constricted space, such as a nozzle, which thereby causes the ejectionof ink from an aperture connected to the confined space onto a relevantprint media. Printing devices utilizing the electro-thermal actuator aremanufactured by manufacturers such as Canon and Hewlett Packard.

[0010] As can be seen from the foregoing, many different types ofprinting technologies are available. Ideally, a printing technologyshould have a number of desirable attributes. These include inexpensiveconstruction and operation, high speed operation, safe and continuouslong term operation etc. Each technology may have its own advantages anddisadvantages in the areas of cost, speed, quality, reliability, powerusage, simplicity of construction operation, durability and consumables.

SUMMARY OF THE INVENTION

[0011] According to one aspect, the present invention provides an inkjetnozzle assembly comprising:

[0012] a nozzle chamber for ink to be ejected, the chamber comprising anink inlet for fluid communication with an ink reservoir and a nozzlethrough which ink from the chamber can be ejected; and,

[0013] at least one thermal actuator for contracting the chamber suchthat ink is ejected through the nozzle.

[0014] According to a second aspect, the present invention provides anink nozzle assembly for an inkjet printer, the nozzle assemblycomprising:

[0015] a nozzle and an actuator for ejecting ink through said nozzle;wherein,

[0016] the actuator comprises a resiliently contractable chamber.

[0017] According to another aspect, the present invention provides anink nozzle assembly for an inkjet printer, the nozzle assemblycomprising:

[0018] a nozzle;

[0019] a nozzle chamber for ink to be ejected through the nozzle, thechamber comprising walls configured to define a first volume within thechamber; and,

[0020] at least one actuator for reconfiguring the walls to define asecond volume less than the first volume.

[0021] There is also disclosed herein an ink jet nozzle assemblyincluding a nozzle chamber formed on a substrate, the nozzle chamberhaving an ink ejection port and a projecting rim formed integrally withthe nozzle chamber about said ink ejection port.

[0022] There is further disclosed herein an ink jet nozzle assemblyincluding:

[0023] a nozzle chamber having an inlet in fluid communication with anink reservoir and a nozzle through which ink from the chamber can beejected;

[0024] the chamber including a fixed portion and a movable portionconfigured for relative movement in an ejection phase and alternaterelative movement in a refill phase;

[0025] an expanding, flexible arm and a rigid arm each connected withthe movable portion and cooperating to effect periodically said relativemovement; and

[0026] the inlet being positioned and dimensioned relative to the nozzlesuch that ink is ejected preferentially from the chamber through thenozzle in droplet form during the ejection phase, and ink is alternatelydrawn preferentially into the chamber from the reservoir through theinlet during the refill phase.

[0027] Preferably the movable portion includes the nozzle and the fixedportion is mounted substrate.

[0028] Preferably the fixed portion includes the nozzle mounted on asubstrate and the movable portion includes a vane unit.

[0029] Preferably a plurality of said vane units arranged around saidink ejection port, said vane units each attached to a said expanding,flexible arm and a said rigid arm such that upon activation, a volume ofink in the nozzle chamber adjacent said ejection port is pressurized soas to cause the ejection of ink from said ink ejection port.

[0030] Preferably said flexible arms comprise a conductive heatermaterial encased within an expansion material having a high coefficientof thermal expansion.

[0031] Preferably said conductive heater material is constructed so asto form a concertina upon expansion of said expansion material.

[0032] Preferably said heater material is of a serpentine form and formsa concertina upon heating so as to allow substantially unhinderedexpansion of said expansion material during heating.

[0033] Preferably said vane units are arranged annularly around said inkejection port.

[0034] Preferably said vane units operate as an iris around said inkejection port.

[0035] Preferably the vane units are of a semi-circular form.

[0036] Preferably the assembly comprises four said vane units.

[0037] Preferably said expansion material comprises substantiallypolytetrafluoroethylene.

[0038] Preferably said conductive heater material comprisessubstantially copper.

[0039] Preferably an outer surface of said chamber includes a pluralityof etchant holes provided so as to allow a rapid etching of sacrificiallayers during construction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Notwithstanding any other forms which may fall within the scopeof the present invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

[0041]FIG. 1 is a perspective view of the actuator portions of a singleink jet nozzle in a quiescent position, constructed in accordance withthe preferred embodiment;

[0042]FIG. 2 is a perspective view of the actuator portions of a singleink jet nozzle in a quiescent position constructed in accordance withthe preferred embodiment;

[0043]FIG. 3 is an exploded perspective view illustrating theconstruction of a single ink jet nozzle in accordance with the preferredembodiment;

[0044]FIG. 4 provides a legend of the materials indicated in FIGS. 5 to16;

[0045]FIG. 5 to FIG. 16 illustrate sectional views of the manufacturingsteps in one form of construction of an ink jet printhead nozzle;

[0046]FIG. 17 shows a three dimensional, schematic view of a nozzleassembly for an ink jet printhead in accordance with the invention;

[0047] FIGS. 18 to 20 show a three dimensional, schematic illustrationof an operation of the nozzle assembly of FIG. 17;

[0048]FIG. 21 shows a three dimensional view of a nozzle arrayconstituting an ink jet printhead;

[0049]FIG. 22 shows, on an enlarged scale, part of the array of FIG. 21;

[0050]FIG. 23 shows a three dimensional view of an ink jet printheadincluding a nozzle guard;

[0051]FIGS. 24a to 24 r show three-dimensional views of steps in themanufacture of a nozzle assembly of an ink jet printhead;

[0052]FIGS. 25a to 25 r show sectional side views of the manufacturingsteps;

[0053]FIGS. 26a to 26 k show layouts of masks used in various steps inthe manufacturing process;

[0054]FIGS. 27a to 27 c show three dimensional views of an operation ofthe nozzle assembly manufactured according to the method of FIGS. 24 and25; and

[0055]FIGS. 28a to 28 c show sectional side views of an operation of thenozzle assembly manufactured according to the method of FIGS. 24 and 25.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

[0056] In the preferred embodiment, there is a provided an ink jetprinthead which includes a series of nozzle arrangements, each nozzlearrangement including an actuator device comprising a plurality ofactuators which actuate a series of paddles that operate in an iris typemotion so as to cause the ejection of ink from a nozzle chamber.

[0057] Turning initially to FIG. 1 to FIG. 3, there is illustrated asingle nozzle arrangement 10 (FIG. 3) for the ejection of ink from anink ejection port 11. The ink is ejected out of the port 11 from anozzle chamber 12 which is formed from 4 substantially identical irisvanes 14. Each iris vane 14 is operated simultaneously to cause the inkwithin the nozzle chamber 12 to be squeezed out of the nozzle chamber12, thereby ejecting the ink from the ink ejection port 11.

[0058] Each nozzle vane 14 is actuated by means of a thermal actuator 15positioned at its base. Each thermal actuator 15 has two arms namely, anexpanding, flexible arm 25 and a rigid arm 26. Each actuator is fixed atone end 27 and is displaceable at an opposed end 28. Each expanding arm25 can be constructed from a polytetrafluoroethylene (PTFE) layer 29,inside of which is constructed a serpentine copper heater 16. The rigidarm 26 of the thermal actuator 15 comprises return trays of the copperheater 16 and the vane 14. The result of the heating of the expandablearms 25 of the thermal actuators 15 is that the outer PTFE layer 29 ofeach actuator 15 is caused to bend around thereby causing the vanes 14to push ink towards the centre of the nozzle chamber 12. The serpentinetrays of the copper layer 16 concertina in response to the high thermalexpansion of the PTFE layer 29. The other vanes 18-20 are operatedsimultaneously. The four vanes therefore cause a general compression ofthe ink within the nozzle chamber 12 resulting in a subsequent ejectionof ink from the ink ejection port 11.

[0059] A roof 22 of the nozzle arrangement 10 is formed from a nitridelayer and is supported by posts 23. The roof 22 includes a series ofholes 24 which are provided in order to facilitate rapid etching ofsacrificial materials within lower layers during construction. The holes24 are provided of a small diameter such that surface tension effectsare sufficient to stop any ink being ejected from the nitride holes 24as opposed to the ink ejection port 11 upon activation of the iris vanes14.

[0060] The arrangement of FIG. 1 can be constructed on a silicon waferutilizing standard semi-conductor fabrication andmicro-electro-mechanical systems (MEMS) techniques. For a generalintroduction to a micro-electro mechanical system (MEMS) reference ismade to standard proceedings in this field including the proceedings ofthe SPIE (International Society for Optical Engineering), volumes 2642and 2882 which contain the proceedings for recent advances andconferences in this field. The nozzle arrangement 10 can be constructedon a silicon wafer and built up by utilizing various sacrificialmaterials where necessary as is common practice with MEMS constructions.Turning to FIG. 3, there is illustrated an exploded perspective view ofa single nozzle arrangement 10 illustrating the various layers utilizedin the construction of a single nozzle. The lowest layer of theconstruction comprises a silicon wafer base 30. A large number ofprintheads each having a large number of print nozzles in accordancewith requirements can be constructed on a single large wafer which isappropriately diced into separate printheads in accordance withrequirements. On top of the silicon wafer layer 30 is first constructeda CMOS circuitry/glass layer 31 which provides all the necessaryinterconnections and driving control circuitry for the various heatercircuits. On top of the CMOS layer 31 is constructed a nitridepassivation layer 32 which is provided for passivating the lower CMOSlayer 31 against any etchants which may be utilized. A layer 32 havingthe appropriate vias (not shown) for connection of the heater 16 to therelevant portion of the lower CMOS layer 31 is provided.

[0061] On top of the nitride layer 32 is constructed the aluminium layer33 which includes various heater circuits in addition to vias to thelower CMOS layer.

[0062] Next a PTFE layer 34 is provided with the PTFE layer 34comprising 2 layers which encase a lower copper layer 33. Next, a firstnitride layer 36 is constructed for the iris vanes 14, 18-20 of FIG. 1.On top of this is a second nitride layer 37 which forms the posts andnozzle roof of the nozzle chamber 12.

[0063] The various layers 33, 34, 36 and 37 can be constructed utilizingintermediate sacrificial layers which are, as standard with MEMSprocesses, subsequently etched away so as to release the functionaldevice. Suitable sacrificial materials include glass. When necessary,such as in the construction of nitride layer 37, various othersemi-conductor processes such as dual damascene processing can beutilized.

[0064] One form of detailed manufacturing process which can be used tofabricate monolithic ink jet printheads operating in accordance with theprinciples taught by the present embodiment can proceed utilizing thefollowing steps:

[0065] 1. Using a double sided polished wafer, complete drivetransistors, data distribution, and timing circuits using a 0.5 micron,one poly, 2 metal CMOS process. The wafer is passivated with 0.1 micronsof silicon nitride. Relevant features of the wafer at this step areshown in FIG. 5. For clarity, these diagrams may not be to scale, andmay not represent a cross section though any single plane of the nozzle.FIG. 4 is a key to representations of various materials in thesemanufacturing diagrams, and those of other cross referenced ink jetconfigurations.

[0066] 2. Deposit 1 micron of sacrificial material (e.g. aluminum orphotosensitive polyimide)

[0067] 3. Etch the sacrificial layer using Mask 1. This mask defines thenozzle chamber posts 23 and the actuator anchor point. This step isshown in FIG. 6.

[0068] 4. Deposit 1 micron of PTFE.

[0069] 5. Etch the PTFE, nitride, and oxide down to second level metalusing Mask 2. This mask defines the heater vias. This step is shown inFIG. 7.

[0070] 6. Deposit 1 micron of a conductor with a low Young's modulus,for example aluminum or gold.

[0071] 7. Pattern the conductor using Mask 3. This step is shown in FIG.8.

[0072] 8. Deposit 1 micron of PTFE.

[0073] 9. Etch the PTFE down to the sacrificial layer using Mask 4. Thismask defines the actuators 15. This step is shown in FIG. 9.

[0074] 10. Wafer probe. All electrical connections are complete at thispoint, bond pads are accessible, and the chips are not yet separated.

[0075] 11. Deposit 6 microns of sacrificial material.

[0076] 12. Etch the sacrificial material using Mask 5. This mask definesthe iris paddle vanes 14, 18-20 and the nozzle chamber posts 23. Thisstep is shown in FIG. 10.

[0077] 13. Deposit 3 microns of PECVD glass and planarize down to thesacrificial layer using CMP.

[0078] 14. Deposit 0.5 micron of sacrificial material.

[0079] 15. Etch the sacrificial material down to glass using Mask 6.This mask defines the nozzle chamber posts 23. This step is shown inFIG. 11.

[0080] 16. Deposit 3 microns of PECVD glass.

[0081] 17. Etch to a depth of (approx.) 1 micron using Mask 7. This maskdefines a nozzle rim. This step is shown in FIG. 12.

[0082] 18. Etch down to the sacrificial layer using Mask 8. This maskdefines the roof 22 of the nozzle chamber 12, the port 11, and thesacrificial etch access holes 24. This step is shown in FIG. 13.

[0083] 19. Back-etch completely through the silicon wafer (with, forexample, an ASE Advanced Silicon Etcher from Surface Technology Systems)using Mask 9. This mask defines the ink inlets which are etched throughthe wafer. When the silicon layer is etched, change the etch chemistryto etch the glass and nitride using the silicon as a mask. The wafer isalso diced by this etch. This step is shown in FIG. 14.

[0084] 20. Etch the sacrificial material. The nozzle chambers 12 arecleared, the actuators 15 freed, and the chips are separated by thisetch. This step is shown in FIG. 15.

[0085] 21. Mount the printheads in their packaging, which may be amolded plastic former incorporating ink channels which supply theappropriate color ink to the ink inlets at the back of the wafer.

[0086] 22. Connect the printheads to their interconnect systems. For alow profile connection with minimum disruption of airflow, TAB may beused. Wire bonding may also be used if the printer is to be operatedwith sufficient clearance to the paper.

[0087] 23. Hydrophobize the front surface of the printheads.

[0088] 24. Fill the completed printheads with ink and test them. Afilled nozzle is shown in FIG. 16.

[0089] Referring now to FIG. 17 of the drawings, a nozzle assembly, inaccordance with a further embodiment of the invention is designatedgenerally by the reference numeral 110. An ink jet printhead has aplurality of nozzle assemblies 110 arranged in an array 114 (FIGS. 21and 22) on a silicon substrate 116. The array 114 will be described ingreater detail below.

[0090] The assembly 110 includes a silicon substrate or wafer 116 onwhich a dielectric layer 118 is deposited. A CMOS passivation layer 120is deposited on the dielectric layer 118.

[0091] Each nozzle assembly 110 includes a nozzle 122 defining a nozzleopening 124, a connecting member in the form of a lever arm 126 and anactuator 128. The lever arm 126 connects the actuator 128 to the nozzle122.

[0092] As shown in greater detail in FIGS. 18 to 20 of the drawings, thenozzle 122 comprises a crown portion 130 with a skirt portion 132depending from the crown portion 130. The skirt portion 132 forms partof a peripheral wall of a nozzle chamber 134 (FIGS. 18 to 20 of thedrawings). The nozzle opening 124 is in fluid communication with thenozzle chamber 134. It is to be noted that the nozzle opening 124 issurrounded by a raised rim 136 which “pins” a meniscus 138 (FIG. 18) ofa body of ink 140 in the nozzle chamber 134.

[0093] An ink inlet aperture 142 (shown most clearly in FIG. 22) isdefined in a floor 146 of the nozzle chamber 134. The aperture 142 is influid communication with an ink inlet channel 148 defined through thesubstrate 116.

[0094] A wall portion 150 bounds the aperture 142 and extends upwardlyfrom the floor portion 146. The skirt portion 132, as indicated above,of the nozzle 122 defines a first part of a peripheral wall of thenozzle chamber 134 and the wall portion 150 defines a second part of theperipheral wall of the nozzle chamber 134.

[0095] The wall 150 has an inwardly directed lip 152 at its free endwhich serves as a fluidic seal which inhibits the escape of ink when thenozzle 122 is displaced, as will be described in greater detail below.It will be appreciated that, due to the viscosity of the ink 140 and thesmall dimensions of the spacing between the lip 152 and the skirtportion 132, the inwardly directed lip 152 and surface tension functionas a seal for inhibiting the escape of ink from the nozzle chamber 134.

[0096] The actuator 128 is a thermal bend actuator and is connected toan anchor 154 extending upwardly from the substrate 116 or, moreparticularly, from the CMOS passivation layer 120. The anchor 154 ismounted on conductive pads 156 which form an electrical connection withthe actuator 128.

[0097] The actuator 128 comprises a first, active beam 158 arrangedabove a second, passive beam 160. In a preferred embodiment, both beams158 and 160 are of, or include, a conductive ceramic material such astitanium nitride (TiN).

[0098] Both beams 158 and 160 have their first ends anchored to theanchor 154 and their opposed ends connected to the arm 126. When acurrent is caused to flow through the active beam 158 thermal expansionof the beam 158 results. As the passive beam 160, through which there isno current flow, does not expand at the same rate, a bending moment iscreated causing the arm 126 and, hence, the nozzle 122 to be displaceddownwardly towards the substrate 116 as shown in FIG. 19 of thedrawings. This causes an ejection of ink through the nozzle opening 124as shown at 162 in FIG. 19 of the drawings. When the source of heat isremoved from the active beam 158, i.e. by stopping current flow, thenozzle 122 returns to its quiescent position as shown in FIG. 20 of thedrawings. When the nozzle 122 returns to its quiescent position, an inkdroplet 164 is formed as a result of the breaking of an ink droplet neckas illustrated at 166 in FIG. 20 of the drawings. The ink droplet 164then travels on to the print media such as a sheet of paper. As a resultof the formation of the ink droplet 164, a “negative” meniscus is formedas shown at 168 in FIG. 20 of the drawings. This “negative” meniscus 168results in an inflow of ink 140 into the nozzle chamber 134 such that anew meniscus 138 (FIG. 18) is formed in readiness for the next ink dropejection from the nozzle assembly 110.

[0099] Referring now to FIGS. 21 and 22 of the drawings, the nozzlearray 114 is described in greater detail. The array 114 is for a fourcolor printhead. Accordingly, the array 114 includes four groups 170 ofnozzle assemblies, one for each color. Each group 170 has its nozzleassemblies 110 arranged in two rows 172 and 174. One of the groups 170is shown in greater detail in FIG. 22 of the drawings.

[0100] To facilitate close packing of the nozzle assemblies 110 in therows 172 and 174, the nozzle assemblies 110 in the row 174 are offset orstaggered with respect to the nozzle assemblies 110 in the row 172.Also, the nozzle assemblies 110 in the row 172 are spaced apartsufficiently far from each other to enable the lever arms 126 of thenozzle assemblies 110 in the row 174 to pass between adjacent nozzles122 of the assemblies 110 in the row 172. It is to be noted that eachnozzle assembly 110 is substantially dumbbell shaped so that the nozzles122 in the row 172 nest between the nozzles 122 and the actuators 128 ofadjacent nozzle assemblies 110 in the row 174.

[0101] Further, to facilitate close packing of the nozzles 122 in therows 172 and 174, each nozzle 122 is substantially hexagonally shaped.

[0102] It will be appreciated by those skilled in the art that, when thenozzles 122 are displaced towards the substrate 116, in use, due to thenozzle opening 124 being at a slight angle with respect to the nozzlechamber 134 ink is ejected slightly off the perpendicular. It is anadvantage of the arrangement shown in FIGS. 21 and 22 of the drawingsthat the actuators 128 of the nozzle assemblies 110 in the rows 172 and174 extend in the same direction to one side of the rows 172 and 174.Hence, the ink droplets ejected from the nozzles 122 in the row 172 andthe ink droplets ejected from the nozzles 122 in the row 174 areparallel to one another resulting in an improved print quality.

[0103] Also, as shown in FIG. 21 of the drawings, the substrate 116 hasbond pads 176 arranged thereon which provide the electrical connections,via the pads 156, to the actuators 128 of the nozzle assemblies 110.These electrical connections are formed via the CMOS layer (not shown).

[0104] Referring to FIG. 23 of the drawings, a development of theinvention is shown. With reference to the previous drawings, likereference numerals refer to like parts, unless otherwise specified.

[0105] In this development, a nozzle guard 180 is mounted on thesubstrate 116 of the array 114. The nozzle guard 180 includes a bodymember 182 having a plurality of passages 184 defined therethrough. Thepassages 184 are in register with the nozzle openings 124 of the nozzleassemblies 110 of the array 114 such that, when ink is ejected from anyone of the nozzle openings 124, the ink passes through the associatedpassage 184 before striking the print media.

[0106] The body member 182 is mounted in spaced relationship relative tothe nozzle assemblies 110 by limbs or struts 186. One of the struts 186has air inlet openings 188 defined therein.

[0107] In use, when the array 114 is in operation, air is chargedthrough the inlet openings 188 to be forced through the passages 184together with ink travelling through the passages 184.

[0108] The ink is not entrained in the air as the air is charged throughthe passages 184 at a different velocity from that of the ink droplets164. For example, the ink droplets 164 are ejected from the nozzles 122at a velocity of approximately 3 m/s. The air is charged through thepassages 184 at a velocity of approximately 1 m/s.

[0109] The purpose of the air is to maintain the passages 184 clear offoreign particles. A danger exists that these foreign particles, such asdust particles, could fall onto the nozzle assemblies 110 adverselyaffecting their operation. With the provision of the air inlet openings88 in the nozzle guard 180 this problem is, to a large extent, obviated.

[0110] Referring now to FIGS. 24 to 26 of the drawings, a process formanufacturing the nozzle assemblies 110 is described.

[0111] Starting with the silicon substrate or wafer 116, the dielectriclayer 118 is deposited on a surface of the wafer 116. The dielectriclayer 118 is in the form of approximately 1.5 microns of CVD oxide.Resist is spun on to the layer 118 and the layer 118 is exposed to mask200 and is subsequently developed.

[0112] After being developed, the layer 118 is plasma etched down to thesilicon layer 116. The resist is then stripped and the layer 118 iscleaned. This step defines the ink inlet aperture 142.

[0113] In FIG. 37b of the drawings, approximately 0.8 microns ofaluminum 202 is deposited on the layer 118. Resist is spun on and thealuminum 202 is exposed to mask 204 and developed. The aluminum 202 isplasma etched down to the oxide layer 118, the resist is stripped andthe device is cleaned. This step provides the bond pads andinterconnects to the ink jet actuator 128. This interconnect is to anNMOS drive transistor and a power plane with connections made in theCMOS layer (not shown).

[0114] Approximately 0.5 microns of PECVD nitride is deposited as theCMOS passivation layer 120. Resist is spun on and the layer 120 isexposed to mask 206 whereafter it is developed. After development, thenitride is plasma etched down to the aluminum layer 202 and the siliconlayer 116 in the region of the inlet aperture 142. The resist isstripped and the device cleaned.

[0115] A layer 208 of a sacrificial material is spun on to the layer120. The layer 208 is 6 microns of photo-sensitive polyimide orapproximately 4 μm of high temperature resist. The layer 208 issoftbaked and is then exposed to mask 210 whereafter it is developed.The layer 208 is then hardbaked at 400° C. for one hour where the layer208 is comprised of polyimide or at greater than 300° C. where the layer208 is high temperature resist. It is to be noted in the drawings thatthe pattern-dependent distortion of the polyimide layer 208 caused byshrinkage is taken into account in the design of the mask 210.

[0116] In the next step, shown in FIG. 24e of the drawings, a secondsacrificial layer 212 is applied. The layer 212 is either 2 μm ofphoto-sensitive polyimide which is spun on or approximately 1.3 μm ofhigh temperature resist. The layer 212 is softbaked and exposed to mask214. After exposure to the mask 214, the layer 212 is developed. In thecase of the layer 212 being polyimide, the layer 212 is hardbaked at400° C. for approximately one hour. Where the layer 212 is resist, it ishardbaked at greater than 300° C. for approximately one hour.

[0117] A 0.2 micron multi-layer metal layer 216 is then deposited. Partof this layer 216 forms the passive beam 160 of the actuator 128.

[0118] The layer 216 is formed by sputtering 1,000 Å of titanium nitride(TiN) at around 300° C. followed by sputtering 50 Å of tantalum nitride(TaN). A further 1,000 Å of TiN is sputtered on followed by 50 Å of TaNand a further 1,000 Å of TiN.

[0119] Other materials which can be used instead of TiN are TiB₂, MoSi₂or (Ti, Al)N.

[0120] The layer 216 is then exposed to mask 218, developed and plasmaetched down to the layer 212 whereafter resist, applied for the layer216, is wet stripped taking care not to remove the cured layers 208 or212.

[0121] A third sacrificial layer 220 is applied by spinning on 4 μm ofphoto-sensitive polyimide or approximately 2.6 μm high temperatureresist. The layer 220 is softbaked whereafter it is exposed to mask 222.The exposed layer is then developed followed by hardbaking. In the caseof polyimide, the layer 220 is hardbaked at 400° C. for approximatelyone hour or at greater than 300° C. where the layer 220 comprisesresist.

[0122] A second multi-layer metal layer 224 is applied to the layer 220.The constituents of the layer 224 are the same as the layer 216 and areapplied in the same manner. It will be appreciated that both layers 216and 224 are electrically conductive layers.

[0123] The layer 224 is exposed to mask 226 and is then developed. Thelayer 224 is plasma etched down to the polyimide or resist layer 220whereafter resist applied for the layer 224 is wet stripped taking carenot to remove the cured layers 208, 212 or 220. It will be noted thatthe remaining part of the layer 224 defines the active beam 158 of theactuator 128.

[0124] A fourth sacrificial layer 228 is applied by spinning on 4 μm ofphoto-sensitive polyimide or approximately 2.6 μm of high temperatureresist. The layer 228 is softbaked, exposed to the mask 230 and is thendeveloped to leave the island portions as shown in FIG. 9k of thedrawings. The remaining portions of the layer 228 are hardbaked at 400°C. for approximately one hour in the case of polyimide or at greaterthan 300° C. for resist.

[0125] As shown in FIG. 24l of the drawing a high Young's modulusdielectric layer 232 is deposited. The layer 232 is constituted byapproximately 1 μm of silicon nitride or aluminum oxide. The layer 232is deposited at a temperature below the hardbaked temperature of thesacrificial layers 208, 212, 220, 228. The primary characteristicsrequired for this dielectric layer 232 are a high elastic modulus,chemical inertness and good adhesion to TiN.

[0126] A fifth sacrificial layer 234 is applied by spinning on 2 μm ofphoto-sensitive polyimide or approximately 1.3 μm of high temperatureresist. The layer 234 is softbaked, exposed to mask 236 and developed.The remaining portion of the layer 234 is then hardbaked at 400° C. forone hour in the case of the polyimide or at greater than 300° C. for theresist.

[0127] The dielectric layer 232 is plasma etched down to the sacrificiallayer 228 taking care not to remove any of the sacrificial layer 234.

[0128] This step defines the nozzle opening 124, the lever arm 126 andthe anchor 154 of the nozzle assembly 110.

[0129] A high Young's modulus dielectric layer 238 is deposited. Thislayer 238 is formed by depositing 0.2 μm of silicon nitride or aluminumnitride at a temperature below the hardbaked temperature of thesacrificial layers 208, 212, 220 and 228.

[0130] Then, as shown in FIG. 24p of the drawings, the layer 238 isanisotropically plasma etched to a depth of 0.35 microns. This etch isintended to clear the dielectric from all of the surface except the sidewalls of the dielectric layer 232 and the sacrificial layer 234. Thisstep creates the nozzle rim 136 around the nozzle opening 124 which“pins” the meniscus of ink, as described above.

[0131] An ultraviolet (UV) release tape 240 is applied. 4 μm of resistis spun on to a rear of the silicon wafer 116. The wafer 116 is exposedto mask 242 to back etch the wafer 116 to define the ink inlet channel148. The resist is then stripped from the wafer 116.

[0132] A further UV release tape (not shown) is applied to a rear of thewafer 16 and the tape 240 is removed. The sacrificial layers 208, 212,220, 228 and 234 are stripped in oxygen plasma to provide the finalnozzle assembly 110 as shown in FIGS. 24r and 25 r of the drawings. Forease of reference, the reference numerals illustrated in these twodrawings are the same as those in FIG. 17 of the drawings to indicatethe relevant parts of the nozzle assembly 110. FIGS. 27 and 28 show theoperation of the nozzle assembly 110, manufactured in accordance withthe process described above with reference to FIGS. 24 and 25, and thesefigures correspond to FIGS. 18 to 20 of the drawings.

[0133] It will be understood by those skilled in the art that many otherforms of construction may be possible utilizing a wide range ofmaterials having suitable characteristics without departing from thespirit or scope of the invention as broadly described. The presentembodiment is, therefore, to be considered in all respects to beillustrative and not restrictive.

[0134] The presently disclosed ink jet printing technology ispotentially suited to a wide range of printing systems including: colorand monochrome office printers, short run digital printers, high speeddigital printers, offset press supplemental printers, low cost scanningprinters, high speed pagewidth printers, notebook computers with inbuiltpagewidth printers, portable color and monochrome printers, color andmonochrome copiers, color and monochrome facsimile machines, combinedprinter, facsimile and copying machines, label printers, large formatplotters, photograph copiers, printers for digital photographic‘minilabs’, video printers, PHOTO CD (PHOTO CD is a registered trademark of the Eastman Kodak Company) printers, portable printers for PDAs,wallpaper printers, indoor sign printers, billboard printers, fabricprinters, camera printers and fault tolerant commercial printer arrays.

We claim:
 1. An inkjet nozzle assembly comprising: a nozzle chamber forink to be ejected, the chamber comprising an ink inlet for fluidcommunication with an ink reservoir and a nozzle through which ink fromthe chamber can be ejected; and, at least one thermal actuator forcontracting the chamber such that ink is ejected through the nozzle. 2.An inkjet nozzle assembly according to claim 1 wherein the chamber hasan inlet wall defining the ink inlet, a nozzle wall spaced from theinlet wall, the nozzle wall defining the nozzle, and side walls betweenthe inlet wall and the nozzle wall; and, the at least one thermalactuator moves at least one of the side walls to contract the chamber.3. An inkjet nozzle assembly according to claim 2 wherein the chamberhas four side walls, each of the side walls connected to a respectivethermal actuator.
 4. An inkjet nozzle assembly according to claim 3wherein the four side walls are arcuate vane arranged around a centralaxis, and the thermal actuators are expanding, flexible arms such thatsimultaneous actuation of the arms pushes the arcuate vanes to slidinglyengage each other to contract the chamber.
 5. An inkjet nozzle assemblyaccording to claim 4 wherein said flexible expanding arms comprise aconductive heater material encased within an expansion material having ahigh coefficient of thermal expansion.
 6. An inkjet nozzle assemblyaccording to claim 5 wherein said conductive heater material isconstructed so as to form a concertina upon expansion of said expansionmaterial.
 7. An inkjet nozzle assembly according to claim 5 wherein saidheater material is of a serpentine form and forms a concertina uponheating so as to allow substantially unhindered expansion of saidexpansion material during heating.
 8. An inkjet nozzle assemblyaccording to claim 5 wherein said vanes are arranged annularly aroundsaid nozzle.
 9. An inkjet nozzle assembly according to claim 5 whereinsaid vanes operate as an iris around said nozzle.
 10. An inkjet nozzleassembly according to claim 5 wherein said expansion material comprisessubstantially polytetrafluoroethylene.
 11. An inkjet nozzle assemblyaccording to claim 5 wherein said conductive heater material comprisessubstantially copper.
 12. An ink nozzle assembly for an inkjet printer,the nozzle assembly comprising: a nozzle and an actuator for ejectingink through said nozzle; wherein, the actuator comprises a resilientlycontractable chamber.
 13. An inkjet nozzle assembly according to claim12 wherein said contractable chamber comprises at least one slidablewall.
 14. An inkjet nozzle assembly according to claim 5 wherein said atleast one wall is a side wall and is slidable by thermal actuation. 15.An ink nozzle assembly for an inkjet printer, the nozzle assemblycomprising: a nozzle; a nozzle chamber for ink to be ejected through thenozzle, the chamber comprising walls configured to define a first volumewithin the chamber, and, at least one actuator for reconfiguring thewalls to define a second volume less than the first volume.
 16. Aninkjet nozzle assembly according to claim 15 wherein the walls compriseslidable side walls that reconfigure to define the second volume inresponse to the actuator.
 17. An inkjet nozzle assembly according toclaim 15 wherein the actuator is a thermal actuator.